Personalize the WooCommerce Thank You page

personalize-woocommerce-thank-you-page.php

<?php

add_filter( 'the_title', 'woo_personalize_order_received_title', 10, 2 );
function woo_personalize_order_received_title( $title, $id ) {
    if ( is_order_received_page() && get_the_ID() === $id ) {
	    global $wp;

        // Get the order. Line 9 to 17 are present in order_received() in includes/shortcodes/class-wc-shortcode-checkout.php file
        $order_id  = apply_filters( 'woocommerce_thankyou_order_id', absint( $wp->query_vars['order-received'] ) );
        $order_key = apply_filters( 'woocommerce_thankyou_order_key', empty( $_GET['key'] ) ? '' : wc_clean( $_GET['key'] ) );

        if ( $order_id > 0 ) {
            $order = wc_get_order( $order_id );
            if ( $order->get_order_key() != $order_key ) {
                $order = false;
            }
        }

        if ( isset ( $order ) ) {
            //$title = sprintf( "You are awesome, %s!", esc_html( $order->billing_first_name ) ); // use this for WooCommerce versions older then v2.7
	    $title = sprintf( "You are awesome, %s!", esc_html( $order->get_billing_first_name() ) );
        }
    }
    return $title;
}

You need to pass 2 arguments to the function. One is the title & second is the order id parameter, labelled as $id. It seems you are not passing the 2nd argument.